Insulating bushing



Patented Jan. 12, 1943 UNITED STATES PATENT OFFICE INSULATING BUSHINGApplication July 19, 1940, Serial No. 346,314

2 Olaims. (Cl. 174-167) The present invention relates to insulatingbushings and it has particular relation to electrical insulatingbushings for high-voltage equipment.

It is desirable to have such electrical bushings, and particularly thoseof the high-voltage type, as nearly perfectly sealed as possible againstthe admission of moisture and the egress of oil or other insulatingfluid.

None of the previously suggested sealing means which includes screwcaps, gaskets, and other devices have been found completely satisfactoryfor this purpose. Even a soldered seal arrangement wherein the closingmembers are soldered directly to the ceramic insulating portion is notcompletely satisfactory since the rigid connections are susceptible todamage due to ordinary jars and strains which occur during use.

According to the present invention, a -hermeticaily sealed bushing whichis articularly resistant to such breakage is provided. This improvedconstruction is obtained by providing flexible metallic caps andsupporting members at the sealed joints in a manner hereinafterdescribed in detail.

an improved hermetically sealed electrical insulating bushing.

A further object of the invention is to provide a hermetically sealed,high voltage bushin in which the insulating casing is flexibly supported with respect to other portions of the assembly.

Other objects and advantages will appear from the following detaileddescription taken in conjunction with the accompanying drawing, inwhich:

Figure 1 is an elevational view, partly in section, of an insulatingbushing embodying the invention;

Fig. 2 is a view similar to Fig. l of a modification of the invention;and

Fig. 3 is a sectional view of a cap structure which may be substitutedin the arrangements shown in Figs. 1 and 2.

' The device shown in Figure 1 comprises a tu bular insulating casing 2with surface creepage flanges 4 of a usual type-and having a conduct.-ing member or stud 6 extending axially therethrough. The member 6 may beeither solid or tubular, as preferred and may have a condenser structure3 of alternate layers of conducting and non-conducting material woundabout it in a usual manner. The metallic sleeve I0 is rolled or pressedabout the condenser portion in a manner known to the prior art. A mainsupporting flange l2 for securing the device on the tank of theapparatus with which it is used, is brazed or soldered to the sleeve ID,as shown.

Soldered to the sleeve III at I4 is a lower closure member ii ofrelatively flexible metallic construction. An annular groove I8 isformed near the outer edge of the member 16 in any suitable manner, asby spinning. A ring 20, which may be of the same material as the memberl6 spun to the shape shown, is soldered to the lower portion of thecasing 2 at 22. This soldered connection may be made by firstmetallizing the contacting surface of the casing or in any other mannerwhich will produce a strong bond. The lower end of the ring 20 fits intothe groove l8 and is bonded thereto by filling the groove with solder,as shown at 23. An annular supporting pad 24 is disposed between themember l6 and the lower end of the casing 2 to furnish mechanicalreinforcement for the connect ing assembly. A plug device 25 ispreferably secured to the member IE to permit filling the bushing withinsulating liquid or plastic material.

The upper end of the conductor 8 is screwthreaded as shown at 26 and anut 28 threaded thereon. A flexible metal cap 30, which is preferablyspun from sheet material, is soldered as at 32 to the upper portion ofthe insulated casing 2 while its inner periphery is bent into a groovedportion 33 in the nut 28. The groove 33 is then filled with solder tohermetically seal the joint between the cap and the stud. An additionalnut 34 may be threaded over the outside of the cap to mechanicallyreinforce the soldered Joint.

A plug and cap assembly 35 is secured to the side of the cap 30 topermit testing the level of fluid insulating material in the bushing.This assembly shbuld be such that the test opening may be completelysealed.

In Fig. 2, the invention is shown applied to a somewhat different typeofbushing. This bushing includes a. lower insulating casing portion 36 inaddition to the upper portion 2a and may be filled with oil, porcelain,and other suitable materials. As in the device previously described, aconductor 6a extends through the insulating casing. Flexible metalsupporting members 38 and 40 are soldered to the upper and lower casingsections, respectively, at 42 and H.

- The other ends of these supporting members are shaped, as by spinning,to engage projections 46 upon the metallic supporting flange 48 and aresoldered thereto as indicated at 50. In this manner, the two casingportions are flexibly connected to each other and to thesupporting-flange.

A flexibl metallic member 52 is soldered to the lower end of the lowerinsulating portion 35 at 54. The other end of this member is soldered tothe conductor 6a at 56 to hermetically seal the bottom of the bushing.The member itself may be spun to shape from sheet material.

A flexible cap 38a is soldered to the upper end of thupper portion ofthe casing at 32c and to the conductor to at 58. A testing plug unit 35asimilar to that described in conjunction with Fig. 1 is provided.

The cap assembly employed on the device of Fig. 1 may be substituted forthe simpler arrangement shown in Fig. 2, if desired.

A cap construction having some points or superiority over thosepreviously described is shown in the sectional view in Fig. 3. In thiscase, a nut 62 having an annular shoulder 64 is threaded on the upperend of a conductor 88. The upper, inner portion 68 of this nut isrecessed to form a pocket surrounding some or the screw threads. Theinner edge oi a flexible metallic cap 30b is arranged to seat on theshoulder portion 84 and be soldered or brazed thereto as indicated atHi, to hermetically seal the cap to the nut. The connection of the nutto the conductor is made completely fluid-tight by filling the recess 88with solder 12. A plug assembly 35?: is secured to the side of the cap3017.

It will be evident that the construction illustrated provides a bushingwhich, in addition to being completely sealed against moisture is alsosimple and relatively inexpensive to manufacture. The flexible casingconnections at the top, flange and bottom of the bushing permit relativeexpansion between the portions of the bushing without causing harmfulstresses to be set up. In addition, jars will be absorbed or cushionedthereby preventing undue strain on the porcelain soldered seal joints.

Since various modifications of the embodiments shown will appear tothose skilled in the art, it is intended that the invention shall not belimited except as by the apmnded claims interpreted in View of the priorart.

We claim as our invention:

1. An insulating bushing comprising a tubular insulating casing, aconducting stud extending axially therethrough in spaced relationshiptherewith, insulating material disposed about the central portion ofsaid conducting stud, a metallic sleeve closely surrounding the centralportion or said insulating material, a flexible metallic cap secured insolder sealed relationship to the top or said casing and to saidconducting stud to hermetically close the top of said casing andresiliently space it from said conducting stud, a flexible metallicclosure member soldered to the outer surface 0! said casing at the lowerend thereof and to said metallic sleeve to resiliently support saidcasing in spaced relationship to said sleeve and hermetically seal thespace therebetween, means disposed between said flexible closure memberand the lower edge of said casing to additionally support the casingthereon, and a supporting flange secured to said sleeve. said casingbeing so spaced from said stud and sleeve that transverse forces exertedon said casing are transmitted to said stud only through said flexiblecap and said flexible closure member.

2. A high voltage insulating bushing comprising a tubular insulatingcasing, a conducting stud.

, extending axially therethrough in spaced relationship therewith, aninsulating member disposed about substantially the central portion ofsaid conducting stud, a metallic sleeve surrounding said insulatingmember, a flexible metallic in said groove to resiliently support thecasing,

and means for securing said band to said ring member in solder sealedrelationship tohermetically seal the bottom of said casing.

All"

GORDON A.

JS H. FRAKES.

